Crystal oscillator problems can be frustrating to diagnose. This guide provides a systematic troubleshooting approach for common crystal issues.

Problem: Crystal Not Oscillating

Checklist:

  • Verify polarity (if applicable)
  • Check load capacitance values
  • Measure crystal ESR
  • Verify MCU oscillator configuration
  • Check PCB layout
  • Test with known good crystal

    • Common Causes:

    • Wrong load capacitance (most common)
    • Excessive ESR for the frequency
    • Insufficient drive from oscillator circuit
    • PCB layout issues (long traces, poor grounding)
    • Crystal damage from ESD or mechanical stress

    Problem: Frequency Offset

    Checklist:

  • Measure actual frequency with frequency counter
  • Verify load capacitance calculation
  • Check for stray capacitance
  • Verify crystal calibration

    • Common Causes:

    • Incorrect load capacitance
    • Unaccounted stray capacitance
    • Temperature effects
    • Crystal aging

    Problem: Intermittent Operation

    Checklist:

  • Check across temperature range
  • Verify power supply stability
  • Check for noise coupling
  • Measure oscillator margin

    • Common Causes:

    • Marginal oscillator design
    • Temperature sensitivity
    • Power supply noise
    • Mechanical vibration

    Measurement Techniques

    Frequency Measurement

    • Use high-impedance frequency counter
    • Avoid loading the circuit
    • Use 10:1 probe if oscilloscope needed

    ESR Measurement

    • Use specialized crystal impedance meter
    • Or use network analyzer
    • Compare to datasheet maximum

    Oscillation Verification

    • Use high-impedance oscilloscope probe
    • Check on both crystal pins
    • Verify waveform amplitude

    Quick Tests

    Touch Test

    • Gently touch crystal with finger
    • If oscillation changes or stops, marginal design
    • Indicates insufficient oscillator margin

    Temperature Test

    • Use freeze spray or heat gun
    • Check operation across temperature
    • Identifies temperature sensitivity
    Contact LiTong FAE for troubleshooting support and failure analysis.